In the prior art, a contactless power supply system supplies power in a contactless manner from a power supplying device to a power receiving device (refer to, for example, patent document 1). In recent years, a contactless power supply system has become able to perform contactless power supply with high efficiency. Thus, such type of a contactless power supply has become practical.
For example, there is a method for supplying power in a contactless manner from a power supply to an electric device using electromagnetic induction. This method allows for a cordless structure in which the conventional electric cord is eliminated from between the power supply and the electric device.
In particular, when the power supplying subject is a movable body, there is a great advantage to a contactless power supply since an electric cord, which would inhibit the movement of the movable body, can be omitted. Under the present circumstances, a power supplying subject, which is a movable body, may have the following structure. In the industrial field, a cart supplied with power in a contactless manner may be used in a factory, a clean room, and the like (refer to, for example, patent document 2). Also, in an ID card system, a card held by a person or an object may be placed over a reading machine to supply power from the reading machine to the ID card and perform authentication or the like with the power between the reading machine and the ID card (refer to, for example, patent document 3). Further, there is a concept of laying primary coils in a road at equal intervals to supply power to secondary coils that are coupled to a lower portion of a travelling vehicle (refer to, for example, patent document 4). These structures often use a relatively large primary coil or a number of primary coils to supply power to a single secondary coil arranged in a mobile body.
A contactless transmission device described in patent document 5 is configured such so that a movable device reciprocates relative to a fixed device. The movable device includes secondary coils arranged at fixed intervals in the moving direction of the movable device. The fixed device includes a single primary coil that faces one of the secondary coils. The contactless transmission device is configured so that the primary coil is magnetically coupled to one of the secondary coils regardless of where the movable device is located.